With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
The IEEE 802.11n is a technical standard relatively recently introduced to overcome a limited data rate which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network. More specifically, the IEEE 802.11n supports a high throughput (HT), i.e., a data processing rate of up to above 540 Mbps, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate.
With the widespread use of the WLAN and the diversification of applications using the WLAN, there is a recent demand for a new WLAN system to support a higher throughput than a data processing rate supported by the IEEE 802.11n. A next-generation WLAN system supporting a very high throughput (VHT) is a next version of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLAN systems which have recently been proposed to support a data processing rate of above 1 Gbps in a MAC service access point (SAP).
The next-generation WLAN system supports the transmission of a Multi-User Multiple Input Multiple Output (MU-MIMO) scheme in which a plurality of non-AP STAs accesses a radio channel at the same time in order to efficiently use the radio channel. According to the MU-MIMO transmission scheme, an AP can transmit a frame to one or more MIMO-paired STAs at the same time.
The AP and the plurality of MU-MIMO paired STAs may have different capabilities. In this case, a supportable bandwidth, modulation coding scheme (MCS), forward error correction (FEC), etc., may vary depending on an STA type, usage, channel environment, etc.
According to the MU-MIMO transmission scheme, a transmitter can transmit data to each of a plurality of MU-MIMO paired receivers through at least one or more spatial streams. Herein, a channel between the transmitter and a first receiver and a channel between the transmitter and a second receiver may generate mutual interference. As such, the inter-channel interference between the transmitter and the receiver may obstruct correct data transmission and reception, which may result in decrease in overall throughput of the WLAN system. Accordingly, when data is transmitted by using the MU-MIMO transmission scheme to improve throughput of the WLAN system supporting the MU-MIMO transmission scheme, there is a need to feed back a modulation and coding scheme (MCS) in sequence by considering interference between different channels.
Meanwhile, an environment for transmission and reception between an AP and an STA may be changed. For example, the AP may want to control the number of spatial streams to be transmitted to the STA and send the spatial streams to the STA. Furthermore, the STA may determine that the transmission and reception of data will be optimized by using what spatial streams from among all the spatial streams available between the AP and the STA without being limited to spatial streams allocated by the AP. In this WLAN environment, there is a need for a link adaptation method in which the STA may feed back recommended spatial streams, determined by the STA, and a recommended a Modulation Coding Scheme (MCS) to be applied to the relevant spatial streams to the AP.